The present invention relates to a novel thermochromic composite oxide and a method for detecting temperature or temperature change of a body by using the same. More particularly, the invention relates to a composite oxide exhibiting thermochromic color change at a relatively low temperature and a method for detecting a change in the temperature of a body by using the composite oxide.
Since the temperature at which the color change of the inventive thermochromic composite oxide, referred to as the thermochromic point hereinbelow, takes place is low as compared with most of conventional thermochromic substances, the inventive thermochromic substance is useful as a thermochromic pigment for the purpose of visually detecting the temperature, for example, of a cryopreservation vessel chilled with liquid nitrogen for storage of oval cells used in the techniques of artificial insemination, temperature indication on and leakage detection from pipelines for transfer and reservoir vessels for storage of a liquid at an extremely low temperature such as liquid hydrogen and oxygen as a liquid propellant of rockets and so on in the form of a temperature-sensitive labels and paints. It is also useful for visual monitoring of the temperature distribution in a freezer machine for extremely low temperatures by utilizing the principle of the Joule-Thomson effect and as a thermochromic substance in image-converter devices for conversion of a heat-ray image to a visual image.
Thermochromic substances heretofore known in the art include liquid crystals and certain organic pigments. These thermochromic substances each have a thermochromic point specific to the respective substance exhibiting different colors in the temperature ranges below and above the thermochromic point so that they are widely used for visually detecting a change of temperature between the lower and higher temperature ranges. These conventional thermochromic substances have a problem in that most of them have a thermochromic point at room temperature or at an elevated temperature so that it is eagerly desired to develop a thermochromic substance having a thermochromic point at a low temperature. Moreover these conventional thermochromic substances are unstable at high temperatures as an inherency of organic substances.